This invention concerns sunflower plants and more particularly, sunflower seeds that have developed resistance to sulfonylurea herbicides through mutagenesis.
Cultivated sunflower (Helianthus annuus L.) is a diploid species (2n=34) grown in many temperate, semi-dry regions of the world as a source of oil and confectionery seeds. Oil types of sunflowers contain 40 to 48 percent oil in the seed. Sunflower oil is valued as an edible oil, because of its high unsaturated fat level and light color. Sunflower oil is used for salads, cooking oil or for margarine. The protein content of sunflower meal prepared from seeds after oil extraction is useful as livestock feed. The seeds from both oil and confectionery varieties of cultivated sunflower are useful as bird food.
Only a relatively few herbicides have been found and developed for selective weed control in cultivated sunflower. These herbicides include alachlor, S-ethyl dipropylcarbamothioate (EPTC), ethalfluralin, trifluralin, pendimethalin, chloramben, imazamethabenz-methyl, sethoxydim and sulfentrazone. Additional weed control treatments are needed to provide a better spectrum of weed control and to reduce the development of weed resistance to herbicides.
Among the weeds insufficiently controlled by herbicides presently used in cultivated sunflower are members of the Orobanchaceae family. These weeds are obligate root holoparasites of a number of broadleaf plants, including sunflower. Particular Orobanche species afflicting sunflower include Orobanche aegyptiaca Pers., O. ramosa L., O. minor Sm., O. cumana Wallr. and O. cernua Loefl. O. cumana Wallr. and O. cernua Loefl. (alternative names for the same species) is a severe pest in sunflower in eastern Europe and has been spreading through southern Europe. Orobanche presents a worldwide risk, and some species such as O. minor have appeared as exotics in the United States. Orobanche species are very difficult to eliminate, because, except for their flower parts, they live in the soil, and their seeds are minute, prolifically produced, easily dispersed and very long-lived. Thus, herbicides presently used in sunflower generally provide inadequate control.
Since the discovery of sulfonylurea herbicides over twenty years ago, over two dozen sulfonylureas have been commercially developed for selective weed control in a wide variety of crops (The Pesticide Manual, Eleventh Edition, C. D. S. Tomlin, ed., British Crop Protection Council, Surrey, U.K., 1997). Sulfonylurea herbicides have as an essential molecular structural feature a sulfonylurea moiety (xe2x80x94S(O)2NHC(O)NH(R)xe2x80x94). The sulfonyl end of the moiety is connected either directly or by way of an oxygen atom or an optionally substituted amino or methylene group to a cyclic or acyclic group. At the opposite end of the sulfonylurea bridge, the amino group, which may have a substituent such as methyl (R being CH3) instead of hydrogen, is connected to a heterocyclic group, typically a symmetric pyrimidine or triazine ring, having one or two substituents such as methyl, ethyl, methoxy, ethoxy, methylamino, dimethylamino, ethylamino and the halogens. As the mode of action of sulfonylurea herbicides is inhibition of the enzyme acetolactate synthase (ALS) found in plants but not animals, sulfonylurea herbicides provide a valued combination of excellent efficacy against weeds and very low toxicity to animals.
While sulfonylureas have been developed for selective weed control in a variety of crops, ordinary varieties of cultivated sunflower are generally insufficiently tolerant for sulfonylureas to be useful for selective weed control in sunflower crops. However, preemergence application of a low dose (2 to 6 g/ha) of chlorsulfuron has been reported to result in 75-85% control of O. cernua with sunflower tolerance (L. Garcxc3xada-Torres et al., Weed Research 1994, 34, 395-402). Although sulfonylurea herbicides have thus been shown to have effect on Orobanche species, the sensitivity of ordinary varieties of sunflowers to sulfonylureas prevents use of higher application rates to give better control of Orobanche. 
Greater application rates of sulfonylurea herbicides could be used to control Orobanche as well as other weed species if varieties of sunflower more resistant to sulfonylureas could be developed. To be easily incorporated in breeding programs combining desirable traits, the trait for sulfonylurea tolerance should be highly heritable (i.e. dominant or semi-dominant). Induced mutagenesis has been used to produce sulfonylurea resistance in soybeans, as discussed in U.S. Pat. No. 5,084,082, but this approach has not been reported for sunflower, which has dissimilar seed morphology compared to soybean. Furthermore because 99% of induced mutations are recessive (W. Gottschalk and G. Wolff Induced Mutations in Plant Breeding, Springer-Verlag, N.Y., 1983, particularly p. 12), dominant mutations are extremely rare. To find dominant herbicide resistance mutations typically requires screening many thousands of mutagenized seeds.
Accordingly there is a need to be able to selectively control Orobanche and other weeds using sulfonylurea herbicides. Applicants have conducted an extensive research program to find dominant or semi-dominant mutant traits providing sulfonylurea resistance in cultivated sunflower.
This invention relates to a method for producing a sunflower line containing a highly heritable trait conferring tolerance to sulfonylurea herbicides, wherein the method comprises: (a) treating sunflower seeds with a mutagenic agent; (b) growing the treated seeds into mature plants to produce second-generation seeds; (c) harvesting the second-generation seeds; (d) germinating the second-generation seeds in the presence of an selectably effective amount of a sulfonylurea herbicide to select for survival only germinated seeds containing a trait conferring tolerance to the sulfonylurea herbicide; and (e) growing a surviving germinated seed into a mature plant to produce through self-pollination seeds of the sunflower line containing the heritable trait.
This invention also relates to a sunflower seed containing a highly heritable trait conferring tolerance to sulfonylurea herbicides, wherein the trait is obtained through mutagenesis. Another embodiment of this invention is a sulfonylurea-tolerant sunflower plant, a part thereof such as pollen or an ovule, or a tissue culture of regenerable cells therefrom, grown from the aforementioned sulfonylurea-tolerant seed. The aforementioned seed and plants may additionally contain other desirable traits, such as resistance to Orobanche parasitism.
Another aspect of the invention is a method for producing inbred sunflower seed having tolerance to sulfonylurea herbicides comprising crossing a first parent sunflower with a second parent sunflower plant and harvesting the resultant inbred seed, wherein the first and second parent sunflower plants have a highly heritable trait conferring tolerance to sulfonylurea herbicides, wherein the trait is obtained through mutagenesis. Related embodiments include an inbred sunflower seed produced by this method and an inbred sunflower plant, or a part thereof such as a seed, produced by growing the inbred seed. Still another aspect of the invention is a method for producing hybrid sunflower seed having tolerance to sulfonylurea herbicides comprising crossing a first parent sunflower with a second parent sunflower plant and harvesting the resultant hybrid sunflower seed, wherein the first or second parent sunflower plant has a highly heritable trait conferring tolerance to sulfonylurea herbicides, wherein the trait is obtained through mutagenesis. Related embodiments include a hybrid sunflower seed produced by this method and a hybrid sunflower plant, or a part thereof such as a seed, produced by growing the hybrid seed.
A further aspect of the invention pertains to a method for controlling undesired vegetation in a crop of the aforementioned sulfonylurea-tolerant sunflower plants, the method comprising applying to the locus of the vegetation an effective amount of a sulfonylurea herbicide. Embodiments of this aspect of the invention include a method for controlling Orobanche species parasitic to sunflower.
Additional aspects of the invention include methods for controlling volunteer sunflower plants in a cereal crop by applying an effective amount of 2,4-dichlorophenoxyacetic acid (2,4-D) and in a sugar beet crop by applying an effective amount of a mixture of triflusulfuron-methyl and phenmedipham to the locus of the vegetation.
In the description and examples that follow, a number of terms are used. To provide a clear and consistent understanding of the specification and claims, including the scope to be given such terms, the following definitions are provided:
xe2x80x9cPlantxe2x80x9d: includes plant cells, plant protoplasts, plant cell tissue cultures from which sunflower plants can be regenerated, plant calli, plant clumps, and plant cells that are intact in plants or parts of plants, such as embryos, pollen, ovules, anthers, petals and other flower and seed parts, leaves, stems and roots including root tips, and the like.
xe2x80x9cVariety or cultivarxe2x80x9d: refers to a group of plants within the species (e.g., Helianthus annuus) which share certain constant characteristics that separate them from the typical form and from other possible varieties within that species. While possessing at least one distinctive trait, a xe2x80x9cvarietyxe2x80x9d is also characterized by a substantial amount of overall variation between individuals within the variety, based primarily upon the Mendelian segregation of traits among the progeny of succeeding generations.
xe2x80x9cLinexe2x80x9d: means a group of plants which display less variation between individuals, generally as a result of several generations of self-pollination. Also, a line can include a group of plants vegetatively propagated from a single parent plant, using tissue or cell culture techniques.
xe2x80x9cSunflower Seedxe2x80x9d: botanically referred to as an xe2x80x9cachenexe2x80x9d; means the combined components the pericarp and embryo.
xe2x80x9cMaintainer Linexe2x80x9d: refers to an isogenic fertile male inbred line counterpart to the CMS line. A maintainer line has a normal cytoplasm, which allows breeding with the CMS line to obtain CMS progeny.
xe2x80x9cCytoplasmic male sterile (CMS) plant or inbred linexe2x80x9d: means a sunflower line that produces no viable pollen, i.e. a male sterile plant. Male sterility is inherited maternally, i.e. the male sterile plant is used as the female parent in a cross with pollen from another sunflower. CMS lines are produced by crossing a recurrent parent inbred line (as male) with a non-recurrent line having a cytoplasmic male sterility trait and then backcrossing to the recurrent line until a male sterile line that is homologous to the recurrent line in all other respects is developed. The recurrent line is then considered the maintainer. CMS lines are also referred to as female lines.
xe2x80x9cRestorer Linexe2x80x9d: means a line possessing the gene or genes to restore male fertility or viable pollen to a sunflower hybrid or inbred line and progeny having a maternal cytoplasm that causes male sterility. This term along with a description of cytoplasmic male sterility is discussed by Fick, xe2x80x9cBreeding and Genetics,xe2x80x9d in Sunflower Science and Technology, J. F. Carter ed., 1978, pp. 279-338.
The present invention pertains to sunflower lines having rare highly heritable sulfonylurea herbicide-tolerance traits obtained through chemically or physically induced mutagenesis and artificial selection. These lines are useful in developing commercial varieties of sunflower crops having resistance to sulfonylureas, and thus enable use of these effective and environmentally benign herbicides to selectively control undesired vegetation. Undesired vegetation that can be controlled by sulfonylurea herbicides in resistant sunflower varieties includes troublesome parasitic weeds such as Orobanche species.
Mutagenesis of sunflower can be induced by treatment with a variety of mutagenic agents known in the art, including physical mutagens such as X-rays, gamma rays, fast or thermal neutrons, protons, and chemical mutagens such as ethyl methanesulfonate (EMS), diethyl sulfate (DES), ethyleneimine (EI), propane sultone, N-methyl-N-nitrosourethane (MNU), N-nitroso-N-methylurea (NMU), N-ethyl-N-nitrosourea (ENU) and sodium azide.
Sunflower mutants resistant to sulfonylurea herbicides are then selected by treatment with a selectably effective amount one or more sulfonylurea herbicides. Many sulfonylurea herbicides can be used in selection treatments, including commercially used sulfonylurea herbicides such as amidosulfuron, azimsulfuron, bensulfuron-methyl, chlorimuron-ethyl, chlorsulfuron, cinosulfuron, cyclosulfamuron, ethametsulfuron-methyl, ethoxysulfuron, flupyrsulfuron-methyl, flazasulfuron, foramsulfuron, halosulfuron-methyl, imazosulfuron, iodosulfuron-methyl, mesosulfuron, metsulfuron-methyl, nicosulfuron, oxasulfuron, primisulfuron-methyl, prosulfuron, pyrazosulfuron-ethyl, rimsulfuron, sulfometuron-methyl, thifensulfuron-methyl, triasulfuron, tribenuron-methyl, trifloxysulfuron and triflusulfuron-methyl. A selectably effective amount is the amount of sulfonylurea herbicide that prevents growth of sunflower plants lacking a dominant or semi-dominant mutation conferring resistance to sulfonylurea herbicides. A selectably effective amount will depend upon the sulfonylurea herbicide used as selection agent and can be easily determined by testing using a gradation of sulfonylurea herbicide concentrations. The choice of selection herbicide will influence the spectrum of sulfonylurea herbicide resistance of the selected mutants, although cross-resistance is typical and some selected mutants may be more tolerant of other sulfonylurea herbicides than the sulfonylurea herbicide used as the selection agent. For efficient selection, sulfonylureas with strong activity against ordinary sunflower varieties are desirable. Thifensulfuron-methyl and metsulfuron-methyl work well for selecting sulfonylurea-resistant sunflower mutants.
Finding dominant herbicide resistance mutations typically requires screening many tens to hundreds of thousands of mutagenized seeds. Although such screening can be conducted using a variety of equipment and procedures known in the art, the xe2x80x9cLarge-Scale Hydroponic Screening Systemxe2x80x9d described in U.S. Pat. No. 5,084,082 is particularly useful for recovering sunflower mutants resistant to sulfonylurea herbicides.
Many of the following Examples and Tests refer to sunflower inbred lines xe2x80x98HA89Axe2x80x99 and xe2x80x98HA89Bxe2x80x99, collectively comprising xe2x80x98HA89xe2x80x99, alternatively identified as xe2x80x98H89xe2x80x99. (xe2x80x98HA89Axe2x80x99 is alternatively identified as xe2x80x98H89Axe2x80x99, and xe2x80x98HA89Bxe2x80x99 is alternatively identified as xe2x80x98H89Bxe2x80x99.) xe2x80x98HA89xe2x80x99 was created at the U.S. Department of Agriculture""s North Dakota Agricultural Experiment Station at Fargo, and was released to the public in October, 1971. xe2x80x98HA89Axe2x80x99 consists of the cytoplasmic male sterile inbred line of xe2x80x98HA89xe2x80x99; xe2x80x98HA89Bxe2x80x99 is the inbred line maintainer of xe2x80x98HA89Axe2x80x99. xe2x80x98HA89Axe2x80x99 (also referred to as xe2x80x98CMS H89Axe2x80x99, xe2x80x98CMS HA89Axe2x80x99 and xe2x80x98CMS HA89xe2x80x99) is cytoplasmic male sterile based on material of P. Leclercq, xe2x80x9cUne Stxc3xa9rilitxc3xa9 Mxc3xa2le Cytoplasmique Chez le Tournesol,xe2x80x9d Ann. Amxc3xa9lior. Plantes 1969, 19 (2), 99-106. To reproduce xe2x80x98HA89Axe2x80x99 requires the maintainer xe2x80x98HA89Bxe2x80x99.
The following Example 1 illustrates the formation of sunflower lines resistant to sulfonylureas through the process of induced mutagenesis and artificial selection. In this Example, the parent sunflower line used was xe2x80x98HA89Bxe2x80x99.